The present invention relates to a device for on-line control of the fibre direction of a continuous fibre web in a paper or board machine, comprising at least one former including at least one headbox being arranged for delivering a stock, which in the former is formed into said fibre web, through a slice including lips which are movable in relation to each other and define a discharge opening, said device including:                a fibre direction meter arranged downstream the former for measuring the fibre direction of the fibre web;        a predetermined number of actuating members, which are arranged in predetermined positions along said lips for regulating the discharge opening locally as a response to individual control signals, each being a function of measured fibre direction values; and        a control unit, which is arranged for receiving the measured fibre direction values from the fibre direction meter, calculating said control signals, and transmitting the control signals to the actuating members.        
The invention also relates to method for on-line control of the fibre direction of a continuous fibre web in a paper or board machine comprising at least one former including at least one headbox being arranged for delivering a stock, which in the former is formed into said fibre web, through a slice including lips which are movable in relation to each other and define a discharge opening, said method including:                measuring the fibre direction of the fibre web by means of a fibre direction meter arranged downstream the former;        calculating and transmitting individual control signals, each being a function of measured fibre direction values, to a predetermined number of actuating members which are arranged in predetermined positions along the lips for regulating the discharge opening locally as a response to the control signals.        
Within the field of papermaking, it is known to professionals that the fibre direction in a finished paper sheet, i.e. the main orientation of the cellulose fibres in the sheet, influences the sheet properties to a great extent. When manufacturing paper, generally, a uniform distribution of fibre direction along the entire paper web is aimed at, i.e. that the orientation of the fibres is similar in the machine and cross directions of the paper web. For example, it is known that properties of board, such as flatness, stiffness, bending resistance, stretch and printability, are improved by a uniform distribution of fibre direction. Accordingly, a uniform distribution of fibre direction leads to fewer rejections of, and complaints on, the finished paper product.
In accordance with the so-called vector theory within papermaking, the parameters which control the fibre direction are the wire speed, the discharge velocity of the stock and the discharge direction of the stock in relation to the machine direction. It is known to arrange a measurement system in a paper machine in order to measure the fibre direction of the paper web in the cross direction, when the paper web passes the system. The result from such a measurement system is presented usually as a so-called fibre orientation profile, which is a diagram illustrating how the fibre direction varies in the cross direction of the paper web. Based upon the measured fibre direction, working staff can then reduce any variations of fibre direction by means of adjusting the headbox of the paper machine manually, e.g. by means of manual adjustment of the edge valves of the headbox or the discharge ratio, i.e. the ratio of stock discharge velocity/wire speed.
This method of reducing variations of fibre direction, however, is difficult and irrational. Firstly, said manual adjustments are comparatively difficult to predict. Thus, a minor adjustment may result in an uncontrolled change of the fibre direction. Secondly, it is difficult to predict how said adjustments, alone or in combination with each other, influence the fibre direction. Even if the working staff has a long experience of papermaking, the adjustment methodology tends to follow the principle “screw and see”, i.e. the working staff measures the fibre direction and adjusts the headbox indiscriminately in an iterative process until a sufficiently uniform distribution of fibre direction has been obtained. This adjustment method is ineffective, and a considerable time may elapse before an acceptably uniform distribution of fibre direction has been obtained, during which period the manufactured paper web runs the risk of having to be rejected.